Typically, powered devices such as a wireless electronic devices require a wired charger and power source, which is usually an alternating current (AC) power outlet. Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device to be powered. In general, the transmitter uses an antenna or a coupling device to wirelessly transmit energy by means of electromagnetic fields and/or waves such as, for example, electric fields, magnetic fields, radio waves, microwaves, or infrared or visible light waves. The receiver uses another antenna or coupling device to, wirelessly, collect the energy provided by the transmitter.
Depending on a distance between the transmitter and the receiver while the receiver is still able to effectively collect wireless energy from the transmitter, a wireless power transmission system (i.e., a transmitter and a receiver) may be categorized into two major groups: a near-field wireless power transmission system and a far-field wireless power transmission system. The near-field wireless power transmission system generally requires the receiver (the transmitter) to be relatively close or near to the transmitter (the receiver); the far-field wireless power transmission system generally allows the receiver (the transmitter) to be further away from the transmitter (the receiver) when compared to near-field systems. Since the technologies to wirelessly transmit power in the near-field and far-field wireless power transmission systems are essentially different, each of the systems has its respective advantages/disadvantages over the other.